1. Field of the Invention
The present invention relates to a sonar sensor for the underwater detection of submarines and other underwater obstacles. More specifically, the invention relates to a compact, modular sonar for use on the bow of a ship or submarine utilizing flextensional or other compact transducers with high power density, and a separate light-weight receive sensors having good performance, low cost and reduced size and weight compared to other bow mounted long range sonar systems.
2. Description of the Related Art
As is well known in the art, sonars on-board ships and submarines are useful for the detection of submarines and other underwater obstacles. One particular type of such a sonar is mounted in a ship""s or submarine""s bow dome. In general, a bow dome sonar array is a sonar sensor that is mounted on the hull of a ship or submarine and protected by an acoustically transparent window or ellipsoidal dome. See, for example, U.S. Pat. No. 5,400,300 which generally describes a sonar system mounted underwater on the hull of a ship. See also U.S. Pat. No. 5,719,824 which generally describes an underwater domed sonar assembly.
Within the acoustic window of a bow dome sonar assembly are sound wave projecting and receiving transducers. In the field of sonar, projecting transducers generally are used to project an acoustic output signal into a body of water in response to an input electrical signal. Receiving transducers generally are used to receive acoustic waves reflected back to the sonar assembly and generate an output signal in response the reflected acoustic energy.
Prior art bow dome sonars have been known to use a single transducer array for performing both the transmit function and the receive function as described above. A major problem associated with long range (30-40 nautical miles) sonar assemblies of this type is the size and weight of the assembly. The transition of the transducers from the transmit function to the receive function requires a complex switching network that is housed in the ship or submarine. This adds to the cost and weight of the sonar. Also, transporting such enormous assemblies at the bow of a ship decreases the fuel efficiency and operational speed of the ship.
It is an object of this invention to provide a bow dome long range sonar assembly having separate transducer arrays for both the projecting and receiving functions as an alternative to the dual function transducers of the prior art. In such an arrangement, each of the separate arrays are positioned within the acoustic window. Having separate transmit and receive arrays allows for a lighter and more compact bow dome sonar assembly than known from the prior art.
Further, the size of typical prior art long range sonar assemblies for surface ships are so large that they impact the ships hull design required to house them. This decreases the ships range and its operational speed. Also, the extremely heavy (e.g., 30-40 tons), prior art bow dome sonar assemblies require large amounts of energy to drag them through a body of water. The large size and heavy weight of this assembly adversely affects the ship""s hydrodynamics and causes increased drag and a decrease in fuel efficiency.
It is an object of this invention to provide a bow dome sonar assembly that will give similar high performance as prior art designs in a much smaller package at considerable savings in weight and cost. This design, having separate transmitting and receive arrays, is a narrower and more compact bow dome design than the prior art. Further, it fits much better into the hydrodynamically desirable bulbous bow design which is narrower and taller in shape as compared to a typical sonar bow dome design. This design also eliminates the need for a complex switching network, and receive cabinets, and allows the use of imbedded towed array telemetry because separate transducers are used for the transmit and receive function. Also, the volumetric design of the receive array forms its own virtual baffle and discriminates against reflections from the ship""s or submarine""s structure.
The invention provides a sonar assembly comprising:
a) an elongated array of sequentially juxtaposed transmitting transducer elements stacked within and confined by a pressure housing, each transducer being independently connected to drive circuitry;
b) opposite ends of the pressure housing being attached internally to first and second portions of a frame, which frame is mountable on a ship or submarine;
c) a plurality of staves sequentially positioned around a periphery of the frame, each stave extending between the first and second portions of the frame;
d) a series of acoustic receive hydrophones positioned along each stave, each hydrophone being independently connected to signal detecting circuitry; and
e) an acoustically transparent housing encapsulating the frame.
The invention also provides a bow dome sonar assembly for connection to the bow of a ship or submarine comprising:
a) an elongated array of sequentially juxtaposed transmitting transducer elements stacked within and confined by a pressure housing, each transducer being independently connected to drive circuitry;
b) opposite ends of the pressure housing being attached internally to first and second portions of a frame, which frame is mountable on a ship or submarine;
c) a plurality of staves sequentially positioned around a periphery of the frame, each stave extending between the first and second portions of the frame;
d) a series of acoustic receive hydrophones positioned along each stave, each hydrophone being independently connected to signal detecting circuitry; and
e) an acoustically transparent housing encapsulating the frame.
The invention further provides a process for detecting underwater objects comprising:
a) providing a sonar assembly comprising:
i) an elongated array of sequentially juxtaposed transmitting transducer elements stacked within and confined by a pressure housing, each transducer being independently connected to drive circuitry;
ii) opposite ends of the pressure housing being attached internally to first and second portions of a frame, which frame is mountable on a ship or submarine;
iii) a plurality of staves sequentially positioned around a periphery of the frame, each stave extending between the first and second portions of the frame;
iv) a series of acoustic receive hydrophones positioned along each stave, each hydrophone being independently connected to signal detecting circuitry; and
v) an acoustically transparent housing encapsulating the frame;
b) transmitting an acoustic signal from a plurality of transmitting transducer elements into a fluid medium;
c) receiving a reflected acoustic signal via the acoustic receive hydrophones;
d) sampling analog signals received by the hydrophones via sampling means; and
e) generating a digital signal from the analog signals.